Volatile organic compounds (hereinafter “VOCs”) are an important health and environmental concern. Volatile Organic Compounds (VOCs) are organic chemicals that have a high vapor pressure and easily form vapors at normal temperature and pressure. Volatile organic chemicals (VOCs) are emitted as gases from certain solids or liquids. There may be several different VOCs present in one product.
VOCs are emitted by a wide array of coatings including polyurethane topcoats, residential and commercial real estate oil-based and water-based coatings, as well as industrial thermoset baking enamels and finishes that are specifically formulated for use in automotive, transportation, marine, and industrial maintenance markets and in a variety of product finishes. “Coatings” as used herein include architecture coatings; wood furniture and fixture coatings; metal furniture and fixture coatings; metal container and closure coatings; coil, sheet and strip coatings; appliance coatings; automotive and other transportation coatings; aerospace coatings; machinery and equipment coatings; electrical and electronic coatings; paper, plastic, film, and foil coatings, marine paints and coatings; industrial maintenance coatings; auto refinishing coatings, traffic paints; aerosol paints; and other industrial product finishes or the like.
Coating operations release a significant portion of the non-mobile source emissions of volatile organic compounds (VOCs) into the air. Prior studies have indicated that the percentage of VOC emissions from coating operations may be as high as 10-15%. Controlling emissions from these sources is difficult, due to the fact that a large portion of the responsible sources are small, widely distributed facilities. This is particularly true in the automotive refinishing sector. For these operations add-on controls are prohibitively expensive; thus the regulatory focus has been on controlling the VOC content of coatings. National emission standards limit the volatile organic compound content of coatings. For example, national standards for volatile organic compounds (VOCs) in automobile refinishing operations were promulgated in 1998 (United States Federal Register, v. 63). The rule requires coating manufacturers to limit VOC content in the paints they sell; VOC limits for various categories of auto refinishing coatings are shown in Table 1-1. In addition, due to local air pollution problems, many southern California counties in the United States have mandated laws that further reduce the allowable VOC content to 420 g/L (3.5 lb/gal) for automotive refinishing applications. National VOC emission standards for other coating industries are similarly restrictive.
TABLE 1-1Volatile Organic Compound (VOC) Limits for AutomotiveRefinishing Coatings (Federal Register, v. 63)Grams VOCPounds VOCCoating Categoryper literper gallon*Pretreatment Wash Primer7806.5Primer/Primer Surfacer5804.8Primer Sealer5504.6Single/2-stage Topcoats6005.0Topcoats of more than two stages6305.2Multi-colored topcoats6805.7Specialty coatings8407.0*English units are provided for information only. Regulation enforcement will be based on the metric levels.
There are generally three parts to a coating: pigments, the binder (usually a natural or synthetic resin), and one or more solvents. The pigments are usually insoluble powders that may provide color and also help make the paint or coating opaque. The binder or resin is that part of the vehicle which eventually solidifies to form part of the dried paint film or coating. The binder or resin may be based on thermoplastic polymers. The solvent or diluent (often an organic solvent, or water) is that part of the vehicle that is volatile and does not become part of the coating finish. The emission of VOCS from coatings is primarily from the solvents therein. The major function of the solvents is to thin the coating to make it easier to apply by spraying or the like.
There are also exempt solvents. An exempt solvent is a volatile organic compound that does not participate in an atmospheric photochemical reaction to form smog. It can be an organic solvent but it takes so long to react with nitrogen oxides (NOx) in the presence of sunlight that its reactivity is believed to be negligible. Only a small number of exempt solvents are approved for use in paints and coatings. These include acetone, methyl acetate, PCBTF (Oxsol 100), and volatile methyl siloxanes. After application, liquid coatings solidify, leaving the binder and pigment as a colored coating. Depending on the type of binder, this hardening may be a result of processes such as curing, evaporation, cooling, etc.
In recognition of the health and environmental problems caused by VOC emissions in coatings, there have been attempts made to minimize or eliminate the use of VOCs whenever possible. For example, several manufacturers have reformulated their paints and paint additives in an effort to replace or reduce the solvents in order to eliminate or reduce VOCs during compounding or use of the paint or paint additives. Unfortunately, the use of these reformulated paints and paint additives has been limited due to performance issues.
Accordingly, there has been a need for novel reduced-VOC coatings with reduced amounts of solvent to substantially reduce VOCs to improve public health and benefit industries which are facing increased restrictions related to air emissions. There is a still further need for novel reduced-VOC coatings with improved performance characteristics. There is an additional need for alternative coatings with lower VOCs than the current commercial “reduced-VOC” coatings, that do not use exempt solvents and with ASTM and weathering properties comparable to conventional coatings. There is a still further need for novel reduced-VOC coatings with improved resin and solvent compatibility. The present invention fulfills these needs and provides other related advantages.